EP 0 670 199 A1 describes a riveting device for setting blind rivet elements that features a mandrel, wherein the mandrel can be set in rotation in order to screw the blind rivet element on the mandrel. The mandrel is subjected to the rotational movement by a motor, wherein the mandrel is set in rotation until it has carried out a certain number of revolutions, and wherein the number of revolutions is chosen so that the blind rivet element can be securely screwed on the mandrel.
Once the blind rivet element reaches the mouthpiece on the front side of the housing of the riveting device, further rotation of the mandrel is no longer possible and the blind rivet element exerts a load moment upon the mandrel. The generated load moment causes the disengagement of a clutch so that any further transmission of a rotational movement to the mandrel is interrupted. The same motor subsequently generates a retraction movement of the mandrel into the riveting device in order to ultimately produce the plastic deformation in the blind rivet element. The retraction of the mandrel takes place until a drive component reaches a limit switch, the actuation of which causes a reversal of the motor so that the mandrel can be screwed out of the elastically deformed blind rivet element.
The transmission of the rotational movement to the mandrel and the subsequent retraction of the mandrel into the riveting device with only a single motor requires complex gearing because the change-over between the rotational movement and the retraction movement must take place mechanically. Particularly the friction clutch used, which features an engaging and disengaging component, has an elaborate design.
In addition to the elaborate constructive design of the gearing in the riveting device, it is also disadvantageous that the clutch of the threaded spindle only makes it possible to transmit a fixed speed for screwing blind rivet elements on and off the mandrel via the gearing. It would be advantageous in this respect to also allow different speeds of the rotational movement of the mandrel for different thread sizes of blind rivet elements. It may be advantageous, for example, to preselect a very slow speed for screwing the mandrel into the blind rivet element over the first few turns, and to subsequently increase the speed once the thread on the mandrel securely engages into the thread in the blind rivet element in order to quickly screw the blind rivet element on the mandrel. This would lead to an optimized and shortened work cycle during the operation of the riveting device.
Another disadvantage is that the activation of the provided friction clutch requires energy, which is particularly disadvantageous with respect to battery-operated riveting devices because such riveting devices should be able to set as many blind rivet elements as possible with only one battery charge. Yet another disadvantage is that it is not possible to use the full force of the motor for setting the blind rivet elements because a portion of this force is consumed by the clutch. The clutch is also subject to wear so that the clutch may, if applicable, have to be replaced several times over the service life of the riveting device.
It is furthermore disadvantageous that the riveting device is stroke-controlled so that the same path must be traveled for retracting the mandrel into the riveting device during each setting process. Manufacturing tolerances of the blind rivet elements and of the material to be riveted cannot be taken into consideration and may lead to overloading of the thread in the blind rivet element, for example, when aluminum blind rivet elements are used. Another disadvantage is that a portion of the revolutions of the ball screw spindle of the gearing is required to screw the blind rivet element on and off. The gearing must therefore be designed longer and becomes altogether heavier, wherein this is generally undesirable with respect to handheld riveting devices. The riveting device can also only set blind rivet elements with a right-hand or a left-hand thread. A user who wants to set different blind rivet elements with a left-hand thread and a right-hand thread therefore requires an additional riveting device.